The present invention relates in general to electroplating and in particular to a method of compensating operational variations of nominal branch currents in an electroplating bath in order to improve the uniformity of the thickness of layers deposited on the treated articles.
In general a circuit for electroplating a plurality of articles includes an electrolytic bath in which a plurality of articles together with corresponding anode plates are immersed, a source of total current connected via branch conductors to the anodes and to the articles acting as cathodes.
It is desirable to maintain branch currents in all branch circuits substantially at the same magnitude in order to obtain a substantially uniform thickness of galvanically deposited layers on all articles connected as cathodes.
In practice, a multitude of interferences contribute to irregular distribution of branch currents between respective anodes and cathodes. For example the interferences result from differences in contacts of respective anodes and cathodes to the corresponding conductors, from different spacing between respective anodes and cathodes, from differences in activity of anodes or cathodes and from diffferent resistances of the anode and cathodes.
From German DE-OS 29 51 708, a method is known which in order to improve the branch current distribution, employs regulating transistors in each branch circuit of the electroplating bath in order to actively regulate the individual branch currents which are measured by means of measuring resistors. This known circuit has the advantage that within the adjustment of respective regulators a complete compensation or equalization of all branch currents is made possible; the disadvantage of this known circuit is a relatively high cost of the regulating devices and circuitry.